(1) Field of the Invention
The present invention relates to a mesh roller such as Anilox roller, Ami roller, screened roller, and so on which can supply a measured quantity of ink. More particularly, the present invention relates to a specially designed mesh roller adapted for planography.
(2) Description of the Prior Art
Commonly used mesh rollers for a planographic machine are made of copper, copper alloy and the like having a lipophilic property (an affinity for ink, hydrophobic property, and so on). The surface of such mesh roller is formed with many recessed sections in a fine cell form and a protruded section, the residue of the recessed sections. In planography this mesh roller generally functions as follows.
Ink stored in an ink pan is firstly sucked by a fountain roller and then the sucked ink is supplied to the mesh roller from the surface of the fountain roller. The mesh roller is subjected to the scraping of a doctor blade so as to scrape the ink from the surface of the mesh roller. After this scraping some ink remains in the fine cells formed in the surface of the mesh roller. The remaining ink is supplied to a form roller and a plate cylinder.
As is well known, an offset printing process requires water for the plate cylinder in addition to ink. If an ink supplying step is simplified by using the mesh roller, the excess of the supplied water will flow back to the mesh roller surface via an ink supplying roller and thus the excess water will flow into the ink pan. This excess water will dilute the ink and finally make its printing clearness worsen. On the other hand, the surface of the mesh roller should be made of a wear-resistant material such as a chromium treated material to resist the wearing pressure caused by the hard pressing the doctor blade onto the external surface of the mesh roller. The chromium treated surface is hydrophilic, so that the surface attracts water. If the cells of the mesh roller for supplying the ink are filled with this water, the ink can not be constantly supplied to the plate cylinder.
In order to prevent the cells from water-immersing and thus guarantee the constantly measured quantity of ink to be supplied to the plate cylinder, the previous inventions; Japanese Patent Application Publications No. Sho. 58-42463 and 59-204558, have provided cells whose inner surface is treated with a lipophilic material such as copper plating.
Further, another previous invention; Japanese Patent Application Publication No. Sho. 58-56856, has provided an improved mesh roller whose external surface is deposited with a beryllium-copper layer instead of hydrophilic chromium material and the surface layer excluding the cells are subjected to a heat curing treatment to ensure the wear resistance and prevent the external surface from water immersing.
Although the external surface of the mesh roller is treated with a heat-cured lipophilic copper alloy instead of a hydrophilic chromium, this copper alloy treated mesh roller can not improve its durability against the scraping motion of the doctor blade. Therefore this mesh roller requires work time for exchanging or repairing it. This will reduce the working efficiency of this printing process. Thus it is required to treat the surface of the mesh roller with a non-hydrophilic (lipophilic) having a superior durability at least ten times that of conventional types.
In order to provide the wear-resistance to the roll surface conventional arts have commonly employed a ceramic coating on the surafce. For example, USP. No. 4,301,730 has provided an improved manner to ensure the corrision resistance. A ceramic layer is deposited on the surafce of an Anilox roll by means of a flame coating and thereafter the pores of the ceramic layer are sealed with a polymer sealing material.
Also Japanese Patent Application Publication No. Sho. 58-56855 has provided the wear-resistance and lipophilic property to its mesh roller by providing a ceramic layer and immersing oil into the pin holes of the ceramic layer.
Further, Japanese Patent Application Publication No. Sho. 60-44394 has suggest the the surface of a normal type ink roller is coated with a porous ceramic layer by a flame coating and the pores are treated with a lipophilic resin.
However, the surafce of each roller of the above described prior arts is provided with the ultra-hard type ceramic material and the lipophilic material, mixed thereto, such as fluid oil, polymer, resin and the like. Although such lipophilic materials are inherently easy to conduct the sealing treatment, they are inferior to copper or copper alloy with respect to the lipophilic and non-hydrophilic properties required to the mesh roller for a planography. Further, such polymer and resin have a poorer thermal conductivity than the copper or copper alloy, and thus they can not effectively transmit the heat generated by high pressingly scraping motion of the doctor blade. As a result, this heat will raise the temperature of the roller surface. Because of this heat the ink solvent at the roller surface will be evaporated and further the polymer and resin per se will be easily deteriorated by this heat. This phenomenon will make the printing ink unstable and the durability of the printing roller poor. The quality of the printed matters produced by such conventional devices will be also unstable and poor.